1. Field of the Invention
The invention relates to the manufacture of cement clinker in a cement clinker line, and in particular to a plank type conveyor for cooling and conveying cement clinker from a rotary kiln to a clinker outlet of the conveyor.
2. Description of Relevant Art
In cement clinker manufacturing, the cement clinker, briefly clinker, is burnt and sintered in a rotary kiln. The clinker is unloaded from said kiln via a clinker distribution system onto a conveyor grate floor of a clinker cooler. On the grate floor, the clinker forms a layer, as well referred to as clinker bed. The clinker bed is cooled and transported (conveyed) to a clinker outlet of the cooler, e.g. via a crusher for further processing, e.g. milling. The construction of the grate floor is essential as on the one hand cooling air has to be inserted into the clinker bed via the grate floor and on the other hand clinker drop through the grate floor has to be avoided. In addition the clinker has to be transported and the grate floor must withstand the high clinker temperatures and the abrasion caused by moving the clinker over the grate floor be it mechanically or pneumatically.
There are three types of currently used clinker coolers, namely, the first type are stepped grate coolers as disclosed e.g. in U.S. Pat. No. 8,397,654.
The second type of coolers have an essentially plane and static grate surface on which the clinker resides. In the surface are aeration slits for cooling the clinker by injecting a cooling gas into the clinker residing on the surface. The static plane grate surface often has box like pockets and the aeration slits are in the bottom of the pockets. In use the pockets are filled with clinker that is blocked by the pockets' side walls from sliding over the grate, i.e. the pockets' bottoms to reduce wear of the grate surface. Clinker transport takes place by shearing the clinker bed, i.e. the upper part of the clinker bed slides over the clinker in said pockets. To this end clinker pushers are installed between the pockets and reciprocate above the pockets' side walls. This type of coolers are commercially available under the name “Polytrack”, the latter being displayed in DE 10 2006 037 765. The Polytrack cooler has longitudinal tracks below longitudinal slits between rows of the pockets. The tracks support reciprocating horizontal pusher plates covering the longitudinal moving slits between the pockets. The pusher plates have pusher ribs extending vertically and perpendicular to the conveying direction and form pockets for several layers of clinker grains. When moving the pusher plates, the clinker in the pockets moves with the pusher plates. Conveying is obtained by moving the pusher plates forward commonly and retracting them separately.
The third type are coolers which have planks extending in parallel to the conveying direction as disclosed e.g. in DE 10 2010 055 825A, U.S. Pat. No. 8,132,520 or EP 1 475 594 A1. Here, we focus only on this third type of clinker cooler, as well referred to as “plank type cooler”.
A plank type cooler typically has a multitude of planks, one besides of the other with moving gaps in between. The longitudinal orientation of the planks is parallel to the conveying direction and the planks are individually moved forward and backward, i.e. reciprocated parallel to the conveying direction to obtain a forward movement of the clinker bed residing on the up facing surface of the planks. A moving gap is a gaps between adjacent, i.e. neighbored planks thereby enabling the movement of one plank relative to the other plank. Such a plank type cooler is disclosed in U.S. Pat. No. 8,132,520 (the disclosure of which patent document is incorporated herein by reference): The clinker is loaded on a plane up facing surface of the planks, extending parallel to the conveying direction. The clinker transport can be obtained by moving at least some neighbored planks forward commonly, i.e. at the same time and retracting them separately, i.e. one after the other, accordingly there are moving gaps between the planks. The cooling air is inserted via the moving gaps into the clinker bed, to thereby heat the cooling air and cool the clinker.
DE 10 2010 055 825 A1 suggests a different type of plank type clinker cooler: Each plank reciprocates and supports box like inlets, being aligned along the plank. The box like inlets have cooling slots for aeration of the clinker. A layer of clinker remains in the box like inlets while transporting the clinker bed to thereby reduce abrasion of any mechanical part of the planks. In addition, the planks support a small amount of protrusions which may be wedge like or plow like. These protrusions shall periodically churn or circulate the clinker bed, to thereby induce a circulation in its lower part. This circulation shall reduce the formation of air channels in the clinker bed, which are unfavorable for heat recuperation.
EP 1 475 594 A1 discloses a further plank type clinker cooler. The cross sections of the planks resemble an open box like channel and clinker aeration is provided by ventilation slits in the bottom of the channel. The moving gaps between adjacent planks are sealed to avoid clinker drop through. To reduce the conveying speed single planks may be static.